The present invention relates generally to a light string system and more particularly to a light string system employing light emitting diodes (LED's).
The light string system of this invention may be used for decorative purposes, such as, for example, Christmas lights, for signaling purposes, such as for example, traffic and/or pedestrian lights and a number of other applications.
In the past, Christmas tree lights have been made using for the most part either incandescent bulbs or neon lamps. These lights usually come in strings of 25, 50 or 100 bulbs or lamps attached together in a series arrangement. The strings can be plugged into one another up to an allowable power amount. Because the lights are arranged in series, a string of lights will go completely out when one light fails. This problem also occurs when a light loosens up on its socket as the user attaches the string or several strings of lights to a Christmas tree or other fixture.
Light strings of incandescent bulbs tend to burn out rapidly, use a great amount of energy at 115 VAC, and run excessively hot, thus having very unsafe features. A string of neon lamps also runs hot to obtain a good brightness level, uses a good amount of energy at 115 Vac, needs a high value resistor in series to limit the current, and because of its small diameter wiring and its general overall appearance many users get electrical shocks trying to change lamps with the power on.
Incandescent lamps consist of a resistive tungsten filament suspended by support wires with a vacuum inside a glass envelope. They are very susceptible to damage from mechanical shock or vibration and voltage spikes or transients. Generally, the higher the voltage-or, the lower the current at a given voltage the more fragile the filament. Choosing the lowest supply voltage for an incandescent lamp can minimize the effect of shock and vibration. The maximum life rating of incandescent lamps is usually on an average of 10,000 hours and can be increased slightly by derating the lamp and using it below its rated voltage thus diminishing its light output. Incandescent lamp life ratings should be taken with a grain of salt, since they are based only on shock free, vibration free, ripple free testing.
Incandescent lamps can be arranged in parallel as well as in series. If incandescent lamps are used that are rated at 5 volts with a current of 0.115 amps., one lamp would have a resistance of 44 ohms. With a source of 5 volts one lamp would draw a current of 115 milliamps, thus using 0.575 watts of power. If ten of such lamps are arranged in parallel, the total resistance to the source will be 4.4 ohms and the total current will be approximately 1.15 amps, thus using 5.75 watts of power. If 90 more of these same lamps are added, the total resistance to the source will be 0.44 ohms and the total current will be approximately 11.5 amps, thus using 57.5 watts of power. The source now has to supply more than 12 amps of current to feed 100 incandescent lamps at 5 volts. Heat, safety, energy and a unique source supply become big factors in operating such a circuit.
In U.S. Pat. No. 4,675,575 to Smith et al. there is disclosed a light string system having a plurality of mono-color or bi-color light-emitting diodes electrically connected thereto. Each light-emitting diode has a generally elongated, hollow envelope mounted thereover, and the envelope is substantially filled with light conducting optical spheres or even fragments. The envelope may be additionally filed with light-conducting epoxy, light-conducting liquid or light-conducting gas and sealed for improved light transmission and dispersion characteristics. The light-emitting diodes may include an improved base with light-emitting diode leads disposed approximately perpendicular to the axis of the envelope for bulb stability and for enabling the bulb to stand upright on the branches. Both the envelope and the optical spheres include light conducting glass or plastic material. The spheres may be either hollow or spherical and may be of a uniform or a mixed size. Additionally, the balls may be large for stacking in single file within the envelope or centrifuged to the sides of the envelope with the center devoid of spheres. The light emitting diodes may be adapted for use as Christmas tree strings and various AC and DC control circuits are provided for driving the light emitting diodes, for blinking effects, for alternating between two colors, for alternating between three colors, for improving the length of the string and uniformity of intensity of illumination and the like. In a preferred embodiment of the Christmas tree string of lights, a master trunk line and a plurality of limb lines are provided. The limb lines plug into or connect to predetermined locations along the master trunk line for ease of assembly, replacement and the like. this string uses a series-parallel configuration wherein the upper and lower portion of the master trunk line and the individual light-emitting diodes within each limb line are connected in series while the limb line sets are connected in parallel with each other for enabling more lights to be illuminated with less power, for increasing the uniformity of illumination along the length of the string, and for minimizing light outage due to bulb burnout.
It is an object of this invention to provide a new and improved light string system.
It is another object of this invention to provide a light string system using LED's.